(a) Field of the Invention
The present invention relates to a process for sterilization of an enzyme contaminated by bacteria during preservation or repeated use of the enzyme.
(b) Description of the Prior Art
There are many cases where an enzyme is contaminated by bacteria during preservation of the enzyme or repeated use of the enzyme. For instance, during the use of an enzyme dissolved in an aqueous solution, bacteria contaminate the solution, and during the repeated use of a so-called immobilized enzyme, bacteria adhere to the immobilized enzyme to cause the reduction of the enzymatic actitivy.
Particularly, in the case of the immobilized enzyme wherein the substrate of the enzyme has a composition of components favorable to the growth of bacteria, and in the case where the treatment conditions in the use of a immobilized enzyme are environmentally favorable to the growth of the bacteria, the contamination of the enzyme by bacteria becomes significant.
In addition, in the immobilized enzyme which has been contaminated by bacteria, not only the reduction of the enzymatic activity but also the deterioration of the quality of the substrate to which the enzyme has been applied becomes noticeable.
For instance, at present, lactose hydrolyzed whey syrups and lactose hydrolyzed milk are industrially produced by using an immobilized lactase. The immobilized lactase is prepared by bringing lactase, which hydrolyzes lactose in animal's milk into glucose and galactose, into chemical bonding with a water-insoluble carrier, for instance, chitin and resin or by entrapping lactase in cellulose triacetate, polyacrylamide gel, etc.
However, in the utilization of such an immobilized lactase, the immobilized lactase is generally used continuously and repeatedly in the conditions packed within a reactor. Namely, the mode of utilization of the immobilized lactase is different from the batch-wise use of free lactase. Accordingly, in the treatment of the milk even if the sterilized milk is used and the reactor and the mechanical apparatus to which the sterilized milk is brought into contact are to be treated by sterilization, proliferation of microorganisms during the repeated use of the immobilized enzyme packed in the reactor is unavoidable, and as a result of increased number of contaminating bacteria, the quality of the above-mentioned products become deteriorated. Consequently, it becomes unavoidable to limit the number of times of repeated use of the immobilized lactase resulting in disadvantage in cost.
In consideration of the above-mentioned situations, several treatments have been devised in the case of utilization of an enzyme or an immobilized enzyme and, for instance, the raw material is treated under conditions as aseptic as possible or under conditions which are unsuitable for the proliferation of the microorganisms, for instance, at a low temperature below 10.degree. C. or at a high temperature of 60.degree. to 70.degree. C.
However, there are problems of operation and production cost in keeping the enzymatic reaction system under aseptic conditions, and in addition, the enzymatic reaction is not effective and practical in a low temperature range. On the other hand, in a high temperature range, the reduction of enzymatic activity is unavoidable except for specified enzymes such as heat-resistant enzymes, for instance, glucose-isomerase, and the immobilized enzyme thereof.
In addition, as a means of carrying out sterilization of the contaminated enzyme by bacteria or of the substrate system on which the contaminated enzyme reacts or carrying out the removal of bacteria therefrom without reducing the enzymatic activity or inactivating the enzyme, sterilization by a bactericidal agent or removal of bacteria by a membrane filter is considered, however, the application of the bactericidal agent is limited in the utilization of enzymes in the field of foodstuffs, and there is the disadvantage that the removal of bacteria by a membrane filter is difficult to be applied to the substrate system, for instance, milk protein containing colloidal substances except for those substrate systems of a simple composition comprising low-molecular components.
As has been stated above, a practical process for effectively sterilizing the contaminated enzyme by bacteria has not been found.
The present inventors have found that by immersing the enzyme contaminated with bacteria into a polyvalent alcohol, the enzyme can be sterilized effectively without substantially causing the reduction of enzymatic activity thereof or the inactivation thereof, and have attained the present invention.